netdev - Re: [PATCH net-next v2] net/sched: fix false lockdep warning on qdisc root lock

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Message-ID: <CAKa-r6tZkLX8rVRWjN6857PLiLQtp92O114FYEkXn6pu9Mb27A@mail.gmail.com>
Date: Thu, 18 Apr 2024 16:01:29 +0200
From: Davide Caratti <dcaratti@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Maxim Mikityanskiy <maxim@...valent.com>, Victor Nogueira <victor@...atatu.com>
Cc: netdev@...r.kernel.org, renmingshuai@...wei.com, jiri@...nulli.us, 
	xiyou.wangcong@...il.com, xmu@...hat.com, 
	Christoph Paasch <cpaasch@...le.com>
Subject: Re: [PATCH net-next v2] net/sched: fix false lockdep warning on qdisc
 root lock

hello,

On Thu, Apr 18, 2024 at 3:50 PM Davide Caratti <dcaratti@...hat.com> wrote:
>

[...]

> This happens when TC does a mirred egress redirect from the root qdisc of
> device A to the root qdisc of device B. As long as these two locks aren't
> protecting the same qdisc, they can be acquired in chain: add a per-qdisc
> lockdep key to silence false warnings.
> This dynamic key should safely replace the static key we have in sch_htb:
> it was added to allow enqueueing to the device "direct qdisc" while still
> holding the qdisc root lock.
>
> v2: don't use static keys anymore in HTB direct qdiscs (thanks Eric Dumazet)

I didn't have the correct setup to test HTB offload, so any feedback
for the HTB part is appreciated. On a debug kernel the extra time
taken to register / de-register dynamic lockdep keys is very evident
(more when qdisc are created: the time needed for "tc qdisc add ..."
becomes an order of magnitude bigger, while the time for "tc qdisc del
..." doubles).

-- 
davide